JP3467529B2 - Powder release lubricant for mold casting and mold casting method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder mold release lubricant for die casting and a die casting method, and more particularly, to effectively combine organic powder and inorganic powder which decompose or evaporate by heating. Therefore, it is intended to advantageously improve the releasing lubrication performance.

[0002]

2. Description of the Related Art As a powder release lubricant used in a mold casting process, an inorganic powder excellent in heat insulation and heat retention in order to reduce a heat flow rate from a molten metal to a mold,
For example, talc is used. However, in recent years, in order to reduce the manufacturing cost of the release lubricant, there has been a demand for the development of a release lubricant using an inexpensive inorganic powder that does not necessarily have high heat retention.

That is, in the conventional powder mold release lubricant, the heat insulating property of the inorganic substance is utilized for keeping the temperature of the molten metal, but since the inorganic substance having high heat insulating property is limited, it is used for die casting. The freedom of choice of available minerals has been limited. For example, graphite is inexpensive and excellent in solid lubricity, but since it is an electric conductor, heat conduction due to the movement of free electrons is extremely large compared to inorganic substances such as oxides, and there is a problem in heat insulation. It could not be used for applications that require heat insulation and heat retention.

As a solution to the above problem, instead of utilizing the heat insulating property of the inorganic substance itself, a gas generated by decomposing or evaporating the substance constituting the powder is used as a heat insulating boundary layer between the mold and the molten metal. Can be used.
However, it is virtually impossible to form a continuous thin insulating boundary layer between the molten metal flowing in the casting process and the mold only with the gas generated by the decomposition and evaporation of organic matter. .

[0005]

SUMMARY OF THE INVENTION The present invention has been developed in view of the above circumstances, and provides a powder release lubricant which is inexpensive and has excellent release lubrication performance. The purpose is to propose together with the die casting method using.

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the inventors have found that by combining an organic powder and an inorganic powder that decompose or evaporate by heating, We have found that the intended purpose can be achieved advantageously.

That is, by mixing the inorganic powder and the organic powder, the movement of the generated gas is restrained (pinned) by the inorganic compound powder, and as a result, there is no break, thinness and uniformity. It has been determined that an insulating boundary layer is stably formed between the mold or sleeve and the molten metal. Here, the inorganic powder is for pinning the gas generated by evaporation or decomposition of the organic powder to form a thin and uniform heat insulating layer, and as in the conventional case, the heat insulating property is secured. It's not meant to be.

Various methods have been proposed in the past for improving lubricity by mixing powders having different properties.
In such a solid lubricant, there is no example in which the generated gas is positively used to improve the lubricity.

That is, the gist of the present invention is as follows. 1. Organic substance powder that evaporates or decomposes when heated to generate gas, and graphite, kaolinite, and silasvaloo
Carbon, mica, boron nitride, carbon nanotube, carbon
(C ₆₀ ), talc, pyrophyllite, crystalline SiO ₂ , oxide mag
Nesium, zirconium silicate, perlite (pearlite)
And one selected from Vermiculite or
Ri Do from mixed powder of two or more of the inorganic powder, the mixed powder
The blending ratio of the organic powder in the body is 1 g of the mixed powder.
The amount of gas generated is 10 to 50 ml per
A powder release lubricant for die casting, characterized in that the average particle size of the body is 1 to 30 μm .

[0010]

[0011]

[0012]

2. The powder release lubricant described in 1 above is applied to the inner surface of the mold cavity and / or the inner surface of the injection sleeve at a rate of 0.01 to 10 g per unit area 1 m ² , and mixed by contact with the molten metal to be injected. A die casting method characterized in that a gas-solid mixed layer of a gas generated from powder and an inorganic powder is used as an adiabatic boundary layer.

[0014]

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. In the present invention, the gas generated by evaporation and decomposition of the organic substance is used as a means for reducing the heat flow rate from the molten metal to the mold, and therefore the heat insulating property of the inorganic substance itself does not need to be particularly excellent. Therefore, the degree of freedom in powder selection is greatly expanded,
Low cost inorganic powders can be utilized.

As described above, in the present invention, since the inorganic powder functions not as a heat insulating material but as a pinning material for mainly generated gas, there is no problem even if the heat insulating property itself is low, Rather, it is preferable that the solid lubricity is excellent so that adhesion with the mold does not occur. For solid lubricity
The excellent inorganic powder, graphite, kaolinite, shirasu balloons, mica and boron nitride are exemplified
It Further, the inorganic powder is not limited to the above-mentioned ones, but carbon nanotubes, carbon isotopes (C
₆₀ ) , talc, pyrophyllite, crystalline SiO ₂ , magnesium oxide, zirconium silicate, perlite (pearlite) and vermiculite can also be preferably used.

On the other hand, as the organic powder, any one can be used regardless of its kind, as long as it is a solid at room temperature and generates a gas by evaporating or decomposing by heating, and itself is a solid. It does not have to be lubricious in the state. As such an organic powder, polyethylene wax, metal soap (Ca soap, Zn soap, Li soap) or the like is advantageously suitable. In addition, paraffin hydrocarbon, sulfonic acid, sulfonate and the like can also be preferably used.

As described above, when only the organic powder is used as the lubricant, that is, when only the generated gas phase is used, a thin insulating boundary layer without a break is formed between the molten metal and the mold. While it is virtually impossible, according to the present invention, when a mixed powder of an organic powder and an inorganic powder is used as a lubricant, a gas generated by evaporation or decomposition of the organic powder is Since it is pinned with the inorganic powder, a thin and uniform heat insulating layer is formed, and as a result,
Good release lubrication performance is demonstrated.

This mechanism is schematically shown in FIGS. 1 (a) and 1 (b) for comparative explanation. FIG. 1 (a) shows that when a mixed powder of organic powder and inorganic powder according to the present invention is used as a lubricant,
FIG. 1 (b) shows the case where only organic powder is used as the lubricant. As shown in Fig. 1 (b), when only organic powder is used as the lubricant, the generated gas is divided and a thin and seamless heat insulating boundary layer is not formed between the molten metal and the mold. The molten metal and the mold partially contact each other, and heat escapes to the mold. On the other hand, as shown in FIG. 1 (a), when the mixed powder according to the present invention is used as the lubricant, the generated gas is pinned by the inorganic powder, so that the molten metal and the mold are Since a thin insulating boundary layer with no breaks is formed between them, heat does not easily escape to the mold.

In the present invention, if the mixing ratio of the organic powder in the mixed powder is too small, a sufficient heat insulating effect cannot be obtained, while if the mixing ratio is too large, gas entrapment in the molten metal may occur. It is important that the mixing ratio of the powder is such that 10 to 50 ml of gas is generated per 1 g of the mixed powder.

FIG. 2 shows the results of examining the heat insulating effect when graphite is used as the inorganic powder and polyethylene wax is used as the organic powder, in relation to the amount of gas generated per 1 g of the mixed powder. The heat insulating effect was evaluated by the flow length when ² g of the mixed powder per 1 m ² was applied to the surface of the mold and the molten aluminum alloy was poured on the mixed powder. As shown in FIG. 2, a particularly excellent heat insulating effect is obtained when the amount of generated gas per 1 g of the mixed powder is 10 to 50 ml. Particularly preferably, it is 17 to 38 ml.

Incidentally, FIG. 2 also shows the relationship between the flow length of the molten aluminum alloy and the mixing ratio of the polyethylene wax in the mixed powder, but 1 g of the mixed powder required to obtain an excellent heat insulating effect. In order to obtain the generated gas amount of 10 to 50 ml per unit, the polyethylene wax is in the range of 10 to 50 mass%, and more preferable in order to obtain the generated gas amount of 17 to 38 ml, the polyethylene wax is in the range of 17 to 38 mass%. It may be contained in each.

Further, considering the applicability of the mixed powder and the pinning effect of the gas generated by the inorganic powder, the particle size of the inorganic powder in the mixed powder is also important. According to the above, the average particle size of the inorganic powder is 1 to
It was confirmed that good results were obtained when the thickness was 30 μm. The particle size of the organic powder is not particularly limited, but if it is too small, the amount of water molecules adsorbed increases, and as a result, the powder tends to agglomerate and the applicability to the mold decreases. If it is too large, the smoothness of the surface of the casting will be reduced especially for aluminum alloys, making it unsuitable as a product. Therefore, like the inorganic powder, it is preferably about 1 to 30 μm.

Further, when the mixed powder suspension is applied to the inner surface of the mold cavity for casting and the inner surface of the injection sleeve, the coating method is not particularly limited, but for a closed mold. Is introduced into the mold together with the atmosphere using the vacuum suction method and attached to the surface of the mold.On the other hand, for a mold that is open, spray powder mixture or use electrostatic force to the surface of the mold. Advantageously, the method of adhering to.

The coating amount is 0.01 per 1 m ^2.
It is necessary to make the ~10g. Because the coating amount is 0.01
If it is less than g / m ² , sufficient thermal insulation cannot be obtained, while 10
This is because if it exceeds g / m ² , gas entrapment in the melt may occur. Particularly preferably, it is in the range of 0.5 to 2.0 g.
The die casting method in the present invention is a die casting method,
It means all the casting methods such as the gravity casting method and the high pressure casting method in which the casting is performed using a mold.

Thus, according to the present invention, when the mixed powder and the molten metal come into contact with each other in the casting process, a mixed layer of the inorganic powder and the generated gas is provided between the casting metal mold or sleeve and the molten metal. Since a thin and uniform thermal insulation boundary layer consisting of is formed, the molten metal floats above the solid / gas mixture layer and flows into the cavity while flowing without directly contacting the mold or sleeve. Therefore, the heat flow rate from the molten metal to the mold or the injection sleeve can be significantly reduced.

[0027]

Example As the organic powder, polyethylene wax having an average particle size of 5 μm is used, while as the inorganic powder, the average particle size is 5 μm.
11 μm graphite was used and mixed so that the ratio of organic powder in the mixed powder was 25 mass%. This organic substance powder ratio corresponds to about 30 ml of generated gas per 1 g of mixed powder. This mixed powder was introduced into the inside of a mold as shown in FIG. 3 together with the atmosphere using a vacuum suction method, and adhered to the surface of the mold at a rate of ² g / m ² . After that, in this mold,
A 650 ° C molten aluminum alloy was injected.

The heat insulating boundary layer composed of a mixed layer of the generated gas and the inorganic powder is formed by using a part of the mold with transparent quartz glass,
Direct observation was performed using a zoom microscope and ultra-high speed video recording. 4 (a), (b), and (c) show the state over time. As shown in the figure, when the mixed powder according to the present invention is used, the surface of the mold is not It can be seen that a thin and uniform adiabatic boundary layer composed of a mixed layer of powder and generated gas is formed. For comparison, FIGS. 5 (a), (b), and (c) show the results of the investigation of the formation state of the heat insulating boundary layer when only the organic powder was used. As can be seen, in this case, although the molten metal partially floated due to the gas generation, it was in contact with the mold over a wide area.

Next, an experiment was conducted on how thin a cast product could be obtained by the same method as described above. As a result, due to the formation of the heat insulating boundary layer according to the present invention, in the cast aluminum alloy product, the thickness: 0.5 mm, the area: 1 m ²
It was confirmed that it is possible to cast thin and large products.

[0030]

As described above, according to the present invention, by using the mixed powder of the organic powder and the inorganic powder which evaporates or decomposes by heating to generate the gas as the release lubricant, the molten metal and the mold are formed. It is possible to form a thin insulating boundary layer without breaks, which improves the heat retention inside the sleeve and the casting mold, resulting in the production of thin-walled and large-sized castings that were previously difficult to cast. It becomes possible to cast. Further, in the present invention, since the excellent heat insulating property of the generated gas is used, it is not necessary to use an expensive powder having particularly excellent heat insulating property and heat retaining property as the inorganic powder, and therefore, the manufacturing cost is significantly increased. Significant reduction is achieved.

[Brief description of drawings]

FIG. 1 (a) shows the heat insulating layer in the case where a mixed powder of an organic powder and an inorganic powder according to the present invention is used as a lubricant, and (b) is the case where only an organic powder is used as a lubricant. It is the figure which compared and showed the formation condition.

FIG. 2 is a graph showing the relationship between the ratio of the organic powder in the mixed powder and the flow length of the molten aluminum alloy.

FIG. 3 is a casting apparatus used for confirming the presence of a casting mold and a heat insulating boundary layer used in an example of the present invention.

FIG. 4 shows the state of formation of a heat insulating boundary layer composed of a mixed layer of generated gas and inorganic powder and a molten metal and a mold when a mixed powder of organic powder and inorganic powder according to the present invention is used as a lubricant. It is the figure which showed the contact condition with an inner surface.

FIG. 5 is a diagram showing a state of formation of a heat insulating boundary layer due to generated gas and a state of contact between a molten metal and an inner surface of a mold when only organic powder is used as a lubricant.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-92232 (JP, A) JP-A-4-279243 (JP, A) JP-A-4-279244 (JP, A) JP-A-3- 243242 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B22C 3/00

Claims (2)

(57) [Claims] 1. An organic powder which evaporates or decomposes by heating to generate a gas , graphite, kaolinite, and
Lath Balloon, Mica, Boron Nitride, Carbon Nanotube
Bu, carbon isotope (C ₆₀ ), talc, pyrophyllite, crystalline Si
O ₂ , magnesium oxide, zirconium silicate, parley
Choose from pearlite and vermiculite
It consists of a powder mixture of one or more inorganic powders.
The mixing ratio of the organic powder in the mixed powder is
Amount of gas that generates 10 to 50 ml of gas per 1 g of mixed powder,
A powder release lubricant for die casting, wherein the inorganic powder has an average particle size of 1 to 30 μm . 2. The melt for applying the powder release lubricant according to claim 1 to the inner surface of the mold cavity and / or the inner surface of the injection sleeve at a rate of 0.01 to 10 g per 1 m ^{2 of} unit area and pouring. A die casting method, wherein a gas / solid mixed layer of a gas generated from a mixed powder and an inorganic powder by contact with a metal is used as an adiabatic boundary layer.